1. Field of the Invention
The invention relates to a functional device, in particular, an organic electroluminescent device.
2. Description of the Related Art
In recent years, functional devices, in particular, organic electroluminescent devices have been developed.
In organic electroluminescent devices, a thin film material which receives the supply of an electric current so as to be excited, thereby emitting light is used. Since the electroluminescent devices give high-luminance light at a low voltage, the devices have wide latent usages in broad fields which include the fields of cellar phone displays, personal digital assistants (PDAs), computer displays, automobile data displays, TV monitors, and ordinary illuminations. In these fields, the electroluminescent devices have advantages of causing devices to be made thin, light, small-sized, low in consumption power, and so on. Accordingly, the electroluminescent devices are largely expected as the leading role in the market of electronic displays in the future. However, in order to use the electroluminescent devices practically instead of conventional displays in these fields, many technical improvements have been taken up as themes about light emission luminance, color tone, endurance in a wide use environment, cost decrease, mass-productivity, and others.
Organic electroluminescent devices as linear light sources have been desired. Disclosed are, for example, a white light source for liquid crystal backlight, an image sensor, or the like (see, Japanese Patent Application Laid-Open (JP-A) No. 2003-51380); and a linear organic electroluminescent device using a stripe electrode as a light source for scanning exposure, or image-reading (see, for example, JP-A No. 2005-260821). However, as the distance from the electrode terminal increases, a more voltage drop is caused so that the emission intensity becomes lower. Thus, the device has a problem that uniform luminance cannot be obtained. This problem is a basic problem to be much solved in the case of using surface emission.
Suggested is, for example, an attempt of making the thickness of an organic emitting layer larger as the distance from the terminal increases, so as to enhance light emission, thereby compensating for a drop in the emission intensity based on the above-mentioned voltage drop (see, for example, JP-A No. 11-40362). Alternatively, suggested is also an attempt of forming auxiliary wiring and supplying an electric current through the auxiliary wiring, to a light emission layer so as to make the electric current larger as the distance from the terminal increases in this device, thereby compensating for the voltage drop (see, for example, JP-A No. 2002-156633). However, any of these attempts makes the device structure thereof complicated, and is insufficient in practical device production suitability. Accordingly, a more practicable improvement is desired.